Reinvestigation of intramolecular hydrogen bond in malonaldehyde derivatives: An ab initio,AIM and NBO study

The RAHB systems in malonaldehyde and its derivatives at MP2/ 6‐311++G(d,p) level of theory were studied and their intramolecular hydrogen bond energies by using the related rotamers method was obtained. The topological properties of electron density distribution in O? H···O intramolecular hydrogen bond have been analyzed in term of quantum theory of atoms in molecules (QTAIM). Correlations between the H‐bond strength and topological parameters are probed. The results of QTAIM clearly showed that the linear correlation between the electron density distribution at HB critical point and RAHB ring critical point with the corresponding hydrogen bond energies was obtained. Moreover, it was found a linear correlation between the electronic potential energy density, V(r_cp), and hydrogen bond energy which can be used as a simple equation for evaluation of HB energy in complex RAHB systems. Finally, the similar linear treatment between the geometrical parameters, such as O···O or O? H distance, and Lp(O)→σ*_OH charge transfer energy with the intramolecular hydrogen bond energy is observed. © 2010 Wiley Periodicals, Inc., Int J Quantum Chem, 2011     

复合物HNO···H2O2内N-H···O蓝移氢键的理论研究

A theoretical study on the blue-shifted H-bond N-H…O and red-shifted H-bond O-H…O in the complexHNO…H_2O_2 was conducted by employment of both standard and counterpoise-corrected methods to calculate thegeometric structures and vibrational frequencies at the MP2/6-31G(d),MP2/6-31 G(d,p),MP2/6-311 q G(d,p),B3LYP/6-31G(d),B3LYP/6-31 G(d,p) and B3LYP/6-311 G(d,p) levels.In the H-bond N-H…O,the calcu-lated blue shift of N-H stretching frequency is in the vicinity of 120 cm~(-1) and this is indeed the largest theoreticalestimate of a blue shift in the X-H…Y H-bond ever reported in the literature.From the natural bond orbital analy-sis,the red-shifted H-bond O-H…O can be explained on the basis of the dominant role of the hyperconjugation.For the blue-shifted H-bond N-H…O,the hyperconjugation was inhibited due to the existence of significant elec-tron density redistribution effect,and the large blue shift of the N-H stretching frequency was prominently due tothe rehybridization of sp~n N-H hybrid orbital.     

Comparative study of XO···ClF and XS···ClF (X = H,CH3, and F) halogen‐bonded complexes

Quantum chemical calculations have been performed to study the single‐electron halogen bonds in HO···ClF and HS···ClF complexes. The calculation methods have a larger effect on the S···Cl halogen bond than on the O···Cl one. The interaction strength in HO···ClF complex is stronger than that in HS···ClF one, but the presence of methyl group in the halogen acceptor makes the sequence reverse. The methyl group has a greater effect on the S···Cl halogen bond than on the O···Cl one. The charge analyses indicate that the methyl group is electron‐donating and the electron‐donating role in the H₃CS? ClF complex is larger than in the H₃CO? ClF one. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Hydrogen bonding characterization of XH2NH2···HNO(X = B,Al, Ga) complexes: A theoretical investigation

The complexes of XH₂NH₂···HNO(X = B, Al, Ga) are characterized as head to tail with hydrogen bonding interactions. The structural characteristics can be confirmed by atoms in molecules (AIM) analysis, which also provide comparisons of hydrogen bonds strengths. The calculated interaction energies at G2MP2 level show that stability of complexes decrease as BH₂NH₂···HNO > AlH₂NH₂···HNO > GaH₂NH₂···HNO. On the basis of the vibrational frequencies calculations, there are red‐shifts for ν(X1? H) and blue‐shifts for ν(N? H) in the complexes on dihydrogen bonding formations (X1? H···H? N). On hydrogen bonding formations (N? H···O), there are red‐shifts for ν(N? H) compared to the monomers. Natural bond orbital (NBO) analysis is used to discuss the reasons for the ν(X1? H) and ν(N? H) stretching vibrational shifts by hyperconjugation, electron density redistribution, and rehybridization. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Unconventional H‐bonds: SH···N interaction

Quantum calculations at the MP2/aug‐cc‐pVDZ level are used to analyze the SH···N H‐bond in complexes pairing H₂S and SH radical with NH₃, N(CH₃)₃, NH₂NH₂, and NH₂N(CH₃)₂. Complexes form nearly linear H‐bonds in which the S? H covalent bond elongates and shifts its stretching frequency to the red. Binding energies vary from 14 kJ/mol for acceptor NH₃ to a maximum of 22 kJ/mol for N(CH₃)₃ and N(CH₃)₂NH₂. Analysis of geometric, vibrational, and electronic data indicate that the SH···N interaction involving SH is slightly stronger than that in which the closed‐shell H₂S serves as donor. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

GIAO,DFT, AIM and NBO analysis of the N?H···O intramolecular hydrogen‐bond influence on the 1J(N,H) coupling constant in push–pull diaminoenones

In the series of diaminoenones, large high‐frequency shifts of the ¹H NMR of the N? H group in the cis‐position relative to the carbonyl group suggests strong N? H···O intramolecular hydrogen bonding comprising a six‐membered chelate ring. The N? H···O hydrogen bond causes an increase of the ¹J(N,H) coupling constant by 2–4 Hz and high‐frequency shift of the ¹⁵N signal by 9–10 ppm despite of the lengthening of the relevant N? H bond. These experimental trends are substantiated by gauge‐independent atomic orbital and density functional theory calculations of the shielding and coupling constants in the 3,3‐bis(isopropylamino)‐1‐(aryl)prop‐2‐en‐1‐one (12) for conformations with the Z‐ and E‐orientations of the carbonyl group relative to the N? H group. The effects of the N? H···O hydrogen‐bond on the NMR parameters are analyzed with the atoms‐in‐molecules (AIM) and natural bond orbital (NBO) methods. The AIM method indicates a weakening of the N? H···O hydrogen bond as compared with that of 1,1‐di(pyrrol‐2‐yl)‐2‐formylethene (13) where N? H···O hydrogen bridge establishes a seven‐membered chelate ring, and the corresponding ¹J(N,H) coupling constant decreases. The NBO method reveals that the LP(O) →σ*_{N? H} hyperconjugative interaction is weakened on going from the six‐membered chelate ring to the seven‐membered one due to a more bent hydrogen bond in the former case. A dominating effect of the N? H bond rehybridization, owing to an electrostatic term in the hydrogen bonding, seems to provide an increase of the ¹J(N,H) value as a consequence of the N? H···O hydrogen bonding in the studied diaminoenones. Copyright © 2010 John Wiley & Sons, Ltd.     

C?H···N and C?H···O intramolecular hydrogen bonding effects in the 1H, 13C and 15 N NMR spectra of the configurational isomers of 1‐vinylpyrrole‐2‐carbaldehyde oxime substantiated by DFT calculations

According to the ¹H, ¹³C and ¹⁵N NMR spectroscopic data and DFT calculations, the E‐isomer of 1‐vinylpyrrole‐2‐carbaldehyde adopts preferable conformation with the anti‐orientation of the vinyl group relative to the carbaldehyde oxime group and with the syn‐arrangement of the carbaldehyde oxime group with reference to the pyrrole ring. This conformation is stabilized by the C? H···N intramolecular hydrogen bond between the α‐hydrogen of the vinyl group and the oxime group nitrogen, which causes a pronounced high‐frequency shift of the α‐hydrogen signal in ¹H NMR (～0.5 ppm) and an increase in the corresponding one‐bond ¹³C–¹H coupling constant (ca 4 Hz). In the Z‐isomer, the carbaldehyde oxime group turns to the anti‐position with respect to the pyrrole ring. The C? H···O intramolecular hydrogen bond between the H‐3 hydrogen of the pyrrole ring and the oxime group oxygen is realized in this case. Due to such hydrogen bonding, the H‐3 hydrogen resonance is shifted to a higher frequency by about 1 ppm and the one‐bond ¹³C–¹H coupling constant for this proton increases by ～5 Hz. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and Theoretical Study of Intramolecular Hydrogen Bond at Two Possible Positions in Pyrazolo[1,2‐b]phthalazine

Properties of dimethyl 3‐(alkylamino)‐5,10‐dioxo‐5,10‐dihydro‐1H‐pyrazolo[1,2‐b]phthalazine‐1,2‐dicarboxylate and its derivatives were studied by means of ab initio method. NO₂ derivative of title compound was synthesized and the nature of its intramolecular hydrogen bond (HB) was investigated. Furthermore, the topological properties of the electron density distributions for N? H···O intramolecular bridges were analyzed in terms of the Bader theory of atoms in molecules (AIM). The electron density (ρ) and Laplacian (?²ρ) properties, estimated by AIM calculations, indicated that O···H bond possesses low ρ and positive ?²ρ values which are in agreement with electrostatic character of the HBs, whereas N? H bonds have covalent character (?²ρ<0). Moreover, steric effect of the t‐Bu group on structure and topological parameters of pyrazolo[1,2‐b]phthalazine conformers was studied. Finally, the powerful method of Espinosa was used to obtain the H‐bond energy.     

Correlation between proton transfer and 35Cl NQR frequency as well as molecular geometry of chloranilic acid in co‐crystals with some organic bases

Proton transfer in hydrogen‐bonded organic co‐crystals of chloranilic acid with some organic bases was investigated by nuclear quadrupole resonance (NQR) spectroscopy. The ³⁵Cl NQR frequencies of chloranilic acid molecule as well as ¹⁴N NQR frequencies of the organic base molecule were measured with the conventional pulse methods as well as double‐resonance methods, respectively. The extent of proton transfer in the O···H···N hydrogen bond was estimated from Townes–Dailey analysis of the ¹⁴N NQR parameters. The ³⁵Cl NQR frequency and molecular geometry of chloranilic acid are correlated to the extent of proton transfer in the protonation process of the organic base molecule. It is shown that the hydrogen bond affects the π‐electron system of chloranilic acid. Geometry dependence of the O···H···N hydrogen bond, i.e. the H? N valence bond order versus the hydrogen‐bond geometry correlation is also discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

The gas phase hydrogen‐bonded dimers of HOCl: A high‐level quantum chemical study

The O···H? O and Cl···H? O hydrogen bonding interactions were analyzed for HOCl dimers by using B3LYP, MP2, CCSD, and MP4(SDTQ) methods in conjunction with the various basis sets. Five isomers were found for the HOCl dimer. The ZPE and BSSE corrected binding energies were computed at the different levels of theory. At the optimized geometries obtained at CCSD/AUG‐cc‐pVDZ level, energies were re‐evaluated at MP4(SDTQ)/AUG‐cc‐pVTZ and CCSD(T)/cc‐pVTZ levels of theory. We found an average of ?20.9 and ?9.6 kJ/mol for the strength of the O···H and Cl···H hydrogen bonding interactions, respectively. Excitation and vertical ionization energies as well as rotational constants were computed at different levels of theory. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis were used to elucidate the nature of the interactions of HOCl dimers. The interaction energies were decomposed by Morokuma methodology. We have computed Δ_fH°(HOCl) and Δ_fH°(HOCl⁺) using the atomization reactions. The Δ_fH°₂₉₈(HOCl) values are ?17.85 and ?18.05 kcal/mol by using CBS‐Q and CBS‐QB3 extrapolation models, respectively, in good agreement with the results given in JANAF tables. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Theoretical Studies on the Hydrogen‐bonding and π‐Stacking Interactions in the m‐Nisoldipine Polymorphism Dimers

The intermolecular interactions in the dimers of m‐nisoldipine polymorphism were studied by B3LYP calculations and quantum theory of "atoms in molecules" (QTAIM) studies. Four geometries of dimers were obtained: dimer I (a‐dimer, O···H? N), dimer II (b‐dimer, O···H? N), dimer III (b‐dimer, π‐stacking‐c), and dimer IV (b‐dimer, π‐stacking‐p). The interaction energies of the four dimers are along the sequence of II>I>III>IV. The intermolecular distance of the interactions follows the order: I (O···H? N)II>III>IV, and the electrostatic character decreases along the sequence: I>II>III>IV.     

A novel azocompound, 2‐(4‐phenylazoaniline)‐4‐phenylphenol: Spectroscopic and quantum‐chemical approach

A novel azocompound with two nonequivalents azo groups, 2‐(4‐phenylazoaniline)‐4‐phenylphenol, was synthesized and characterized by spectroscopic and computational analysis. An intramolecular hydrogen bonding (HB), ? O₁? H₁ ··· N₁? , involving the ? N₁?N₂? group and the proton in a neighbor hydroxyl moiety, was identified. It was found responsible for a characteristic π‐conjugated H₁? O₁? C₁₈?C₁₃? N₂?N₁? six‐membered cyclic fragment. It is worth noting that this azo group is involved in an azo‐hydrazo equilibrium, being the azo form the most stable one. This resonance‐assisted HB was characterized using the OH‐related infrared bands and the corresponding signals in ¹H NMR. In addition, conformational studies and geometrical and electronic parameter calculations were performed using the density functional theory, at B3LYP/6‐311++G** level. Bond and ring critical points were identified using the atoms in molecules theory, which allowed confirming the intramolecular HB. The second azo‐group cannot be involved in HB, but it also presents two stereoisomerics forms corresponding to cis (Z) and trans (E) configurations, with the later being the one with the lowest energy. © 2013 Wiley Periodicals, Inc.     

Ab initio and AIM studies on typical π‐type and pseudo‐π‐type halogen bonds: Comparison with hydrogen bonds

Series of typical π‐type and pseudo‐π‐type halogen‐bonded complexes B ··· ClY and B ··· BrY and hydrogen‐bonded complex B ··· HY (B = C₂H₄, C₂H₂, and C₃H₆; Y = F, Cl, and Br) have been investigated using the MP2/aug‐cc‐pVDZ method. A striking parallelism was found in the geometries, vibrational frequencies, binding energies, and topological properties between B ··· XY and B ··· HY (X = Cl and Br). It has been found that the lengths of the weak bond d(X ··· π)/d(H ··· π), the frequencies of the weak bond ν(X ··· π)/ν(H ··· π), the frequency shifts Δν(X? Y)/Δν(H? Y), the electron densities at the bond critical point of the weak bonds ρ_c(X ··· π)/ρ_c(H ··· π), and the electron density changes Δρ_c(X? Y)/Δρ_c(H? Y) could be used as measures of the strengths of typical π‐type and pseudo‐π‐type halogen/hydrogen bonds. The typical π‐type and pseudo‐π‐type halogen bond and hydrogen bond are noncovalent interactions. For the same Y, the halogen bond strengths are in the order B ··· ClY < B ··· BrY. For the same X, the halogen bond strength decreases according to the sequence F > Cl > Br that is in agreement with the hydrogen bond strengths B ··· HF > B ··· HCl > B ··· HBr. All of these typical π‐type and pseudo‐π‐type hydrogen‐bonded and halogen‐bonded complexes have the “conflict‐type” structure. Contour maps of the Laplacian of π electron density indicate that the formation of B ··· XY halogen‐bonded complex and B ··· HY hydrogen‐bonded complex is very similar. Charge transfer is observed from B to XY/HY and both the dipolar polarization and the volume of the halogen atom or hydrogen atom decrease on B ··· XY/B ··· HY complex formation. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

F···HO intramolecular hydrogen bond as the main transmission mechanism for 1hJF,H(O) coupling constant in 2′‐fluoroflavonol

Flavonoids are useful compounds in medicinal chemistry and exhibit conformational isomerism, which is ruled by intramolecular interactions. One of the main intramolecular forces governing the stability of conformations is the hydrogen bond. Hydrogen bond involving fluorine covalently bonded to carbon has been found to be rare, but it appears in 2′‐fluoroflavonol, although the F···HO hydrogen bond cannot be considered the main effect governing the conformational stability of this compound. Because ¹⁹F is magnetically active and suitable for NMR studies, the ^1hJ_F,H(O) coupling constant can be used as a probe for such an interaction in 2′‐fluoroflavonol. In fact, the ^1hJ_F,H(O) coupling was computationally analyzed in this work, and the F···HO hydrogen bond was found to be its main transmission mechanism, which modulates this coupling in 2′‐fluoroflavonol, rather than overlap of proximate electronic clouds, such as in 2‐fluorophenol. Copyright © 2012 John Wiley & Sons, Ltd.     

Nature of MoH···I bonds in Cp2Mo(L)H···I‐C≡C‐R Complexes (L=H,CN, PPh2, C(CH3)3; R=NO2, Cl,Br, H,OH, CH3, NH2)

The nature of the MoH···I bond in Cp₂Mo(L)H···I‐C≡C‐R (L= H, CN, PPh₂, C(CH₃)₃; R=NO₂, Cl, Br, H, OH, CH₃, NH₂) was investigated using electrostatic potential analysis, topological analysis of the electron density, energy decomposition analysis and natural bond orbital analysis. The calculated results show that MoH···I interactions in the title complexes belong to halogen‐hydride bond, which is similar to halogen bonds, not hydrogen bonds. Different to the classical halogen bonds, the directionality of MoH···I bond is low; Although electrostatic interaction is dorminant, the orbital interactions also play important roles in this kind of halogen bond, and steric interactions are weak; the strength of H···I bond can tuned by the most positive electrostatic potential of the I atom. As the electron‐withdrawing ability of the R substituent in the alkyne increases, the electrostatic potential maximum of the I atom increases, which enhances the strength of the H···I halogen bond, as well as the electron transfer.     

Molecular dynamics of cis‐1‐(2‐hydroxy‐5‐ methylphenyl)ethanone oxime and N‐(2‐hydroxy‐4‐methylphenyl)acetamide in solution studied by NMR spectroscopy

The formation of hydrogen bonds and molecular dynamics for the molecules cis‐1‐(2‐hydroxy‐5‐methylphenyl)ethanone oxime ( I ) and N‐(2‐hydroxy‐4‐methylphenyl)acetamide ( II ) have been investigated in solution using NMR. The results confirm the formation of O? H···O, O? H···N and O···H? N type inter‐ and intramolecular hydrogen bonds. Spin‐lattice relaxation times (T₁), activation energy of molecular dynamics and energy of intramolecular hydrogen bonds have been determined. Copyright © 2010 John Wiley & Sons, Ltd.     

4‐(4‐Hydro­xy­benzyl­idene­amino)‐4H‐1,2,4‐triazole hemihydrate

In the title compound, 4‐(4H‐1,2,4‐triazol‐4‐yl­imino­methyl)­phenol hemi­hydrate, C₉H₈N₄O·0.5H₂O or (I)·0.5H₂O, mol­ecules of (I) are arranged as layers running along the b axis through intermolecular O—H?N and C—H?O hydrogen bonds. These layers are stabilized by hydrogen‐bonded water mol­ecules to form three‐dimensional networks.     

Time‐dependent density functional theory study on the electronic excited‐state hydrogen‐bonding dynamics of 4‐aminophthalimide (4AP) in aqueous solution: 4AP and 4AP–(H2O)1,2 clusters

The time‐dependent density functional theory (TDDFT) method has been carried out to investigate the excited‐state hydrogen‐bonding dynamics of 4‐aminophthalimide (4AP) in hydrogen‐donating water solvent. The infrared spectra of the hydrogen‐bonded solute?solvent complexes in electronically excited state have been calculated using the TDDFT method. We have demonstrated that the intermolecular hydrogen bond C? O···H? O and N? H···O? H in the hydrogen‐bonded 4AP?(H₂O)₂ trimer are significantly strengthened in the electronically excited state by theoretically monitoring the changes of the bond lengths of hydrogen bonds and hydrogen‐bonding groups in different electronic states. The hydrogen bonds strengthening in the electronically excited state are confirmed because the calculated stretching vibrational modes of the hydrogen bonding C?O, amino N? H, and H? O groups are markedly red‐shifted upon photoexcitation. The calculated results are consistent with the mechanism of the hydrogen bond strengthening in the electronically excited state, while contrast with mechanism of hydrogen bond cleavage. Furthermore, we believe that the transient hydrogen bond strengthening behavior in electroniclly excited state of chromophores in hydrogen‐donating solvents exists in many other systems in solution. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

[DBU‐H]+ and H2o as effective catalyst form for 2,3‐dihydropyrido[2,3‐d]pyrimidin‐4(1H)‐ones: A DFT Study

DFT investigations are carried out to explore the effective catalyst forms of DBU and H₂O and the mechanism for the formation of 2,3‐dihydropyrido[2,3‐d]‐pyrimidin‐4(1H)‐ones. Three main pathways are disclosed under unassisted, water‐catalyzed, DBU and water cocatalyzed conditions, which involves concerted nucleophilic addition and H‐transfer, concerted intramolecular cyclization and H‐transfer, and Dimroth rearrangement to form the product. The results indicated that the DBU and water cocatalyzed pathway is the most favored one as compared to the rest two pathways. The water donates one H to DBU and accepts H from 2‐amino‐nicotinonitrile ( 1 ), forming [DBU‐H]⁺‐H₂O as effective catalyst form in the proton migration transition state rather than [DBU‐H]⁺‐OH^?. The hydrogen bond between [DBU‐H]⁺···H₂O··· 1 ^? decreases the activation barrier of the rate‐determining step. Our calculated results open a new insight for the green catalyst model of DBU‐H₂O. © 2015 Wiley Periodicals, Inc.